Outage performance analysis for relay-assisted UWOC systems over GGD weak turbulence with nonzero boresight pointing errors

In this paper, we mainly investigate the outage performance of serial and parallel relay-assisted underwater wireless optical communication (UWOC) systems based on a newly proposed aggregated underwater fading model. In order to overcome the deficiency of the traditional underwater weak turbulence models, that is, they could not accurately fit the measured data in the laboratory, the generalized gamma distribution (GGD) which has been verified by a series of experiments is chosen for the first time to characterize the weak oceanic turbulence. Then, we establish a new receiving signal model which has integrated the implicit path loss plus multipath propagation effect shown by fading free impulse response (FFIR), GGD weak oceanic turbulence, and nonzero boresight pointing errors. Next, we deduce the closed-form expression of the probability density function (PDF) of the hybrid fading considering GGD weak turbulence and nonzero boresight errors based on the new receiving signal model above through double-exponential Taylor expansion and higher transcendental Whittaker function. Finally, the analytical expressions of the outage probabilities for point-to-point (P2P) link, serial and parallel relay-assisted UWOC systems are further derived respectively under the proposed aggregated channel. Numerical simulations are also provided to validate the accuracy of the theoretical formulae derived above, and to show the effects of the key system parameters on the outage performance of relaying UWOC systems.     

Numerical Convergence of the Block-Maxima Approach to the Generalized Extreme Value Distribution

In this paper we perform an analytical and numerical study of Extreme Value distributions in discrete dynamical systems. In this setting, recent works have shown how to get a statistics of extremes in agreement with the classical Extreme Value Theory. We pursue these investigations by giving analytical expressions of Extreme Value distribution parameters for maps that have an absolutely continuous invariant measure. We compare these analytical results with numerical experiments in which we study the convergence to limiting distributions using the so called block-maxima approach, pointing out in which cases we obtain robust estimation of parameters. In regular maps for which mixing properties do not hold, we show that the fitting procedure to the classical Extreme Value Distribution fails, as expected. However, we obtain an empirical distribution that can be explained starting from a different observable function for which Nicolis et al. (Phys. Rev. Lett. 97(21): 210602, 2006) have found analytical results.     

Absorption linewidth inversion with wavelength modulation spectroscopy

For absorption linewidth inversion with wavelength modulation spectroscopy(WMS), an optimized WMS spectral line fitting method was demonstrated to infer absorption linewidth effectively, and the analytical expressions for relationships between Lorentzian linewidth and the separations of first harmonic peak-to-valley and second harmonic zero-crossing were deduced. The transition of CO_2 centered at 4991.25 cm~(-1) was used to verify the optimized spectral fitting method and the analytical expressions. Results showed that the optimized spectra fitting method was able to infer absorption accurately and compute more than 10 times faster than the commonly used numerical fitting procedure. The second harmonic zero-crossing separation method calculated an even 6 orders faster than the spectra fitting without losing any accuracy for Lorentzian dominated cases. Additionally, linewidth calculated through second harmonic zero-crossing was preferred for much smaller error than the first harmonic peak-to-valley separation method. The presented analytical expressions can also be used in on-line optical sensing applications, electron paramagnetic resonance, and further theoretical characterization of absorption lineshape.     

Physical aspects of magnetized Jeffrey nanomaterial flow with irreversibility analysis

This research presents the applications of entropy generation phenomenon in incompressible flow of Jeffrey nanofluid in the presence of distinct thermal features. The novel aspects of various features, such as Joule heating, porous medium, dissipation features, and radiative mechanism are addressed. In order to improve thermal transportation systems based on nanomaterials, convective boundary conditions are introduced. The thermal viscoelastic nanofluid model is expressed in terms of differential equations. The problem is presented via nonlinear differential equations for which analytical expressions are obtained by using the homotopy analysis method (HAM). The accuracy of solution is ensured. The effective outcomes of all physical parameters associated with the flow model are carefully examined and underlined through various curves. The observations summarized from current analysis reveal that the presence of a permeability parameter offers resistance to the flow. A monotonic decrement in local Nusselt number is noted with Hartmann number and Prandtl number. Moreover, entropy generation and Bejan number increases with radiation parameter and fluid parameter.     

Free-space laser communication performance in the atmospheric channel

In spite of the tremendous technical advancement of available components, the major limitation of free-space laser communication (lasercom) performance is due to the atmosphere, because a portion of the atmospheric path always includes turbulence and multiple scattering effects. Starting from a fundamental understanding of the laser communications system under diverse weather conditions, this chapter provides a comprehensive treatment of the evaluation of parameters needed for analyzing system performance. The significance of higher-order statistics of probability density functions of irradiance fluctuations due to turbulence to performance analysis is explained. Starting from link analysis, the necessary expressions relating link margin, bit-error-rate, signal-to-noise-ratio, and probability of fade statistics are presented. Results for laboratory-simulated atmospheric turbulence and multiple scattering are presented. Example numerical results for simulations of lasercom systems operating under various atmospheric conditions are presented for various scenarios such as uplink-downlink (e.g., between ground and satellite, aircraft or UAV) and horizontal (terrestrial) link. Both turbulence and multiple scattering effects have been included in the analysis with both on-off keying and pulse-position modulation schemes. Statistical estimation and computation of communication parameters presented in this chapter will be useful in designing and optimizing lasercom systems that are reliable under all weather conditions.     

Motional narrowing under diffusion of two spin sub-lattices in LiNaSO4

An expression for the dipolar correlation function characterizing the fluctuations of the Hamiltonian under uncorrelated diffusion of two cationic sub-lattices in a solid has been obtained. A corresponding formula, which can be used for fitting the two-step temperature dependencies of the NMR line width, has been deduced. We also considered the case of a distribution of correlation times and deduced a corresponding analytical fitting function. Elaborated expressions have been applied to the NMR line width analysis of LiNaSO₄ in the temperature range 295–788 K.     

Soliton dynamics of symmetry-endowed two-soliton solutions of the nonlinear Schrodinger equation

A comprehensive analysis is presented of the propagation of symmetry-endowed two-soliton solutions under the influence of various perturbations important in nonlinear optics. Thus, we begin by introducing the analytical expressions of these two-soliton solutions. Then, by considering perturbations which preserve the initial symmetry of the two-soliton solutions, the dependence of the soliton parameters on the propagation distance is determined by using an adiabatic perturbation method. As perturbations of this kind, important for soliton-based communication systems, we consider the bandwidth-limited amplification, nonlinear amplification, and amplitude and phase modulation. Moreover, the results obtained by the adiabatic perturbation method are compared with those obtained by direct numerical simulations of the corresponding governing differential equations. (c) 2000 American Institute of Physics.     

Design and analysis of a GaAs-based 850-nm vertical-cavity surface-emitting laser with different doping in the reflection regions

The present paper deals with the analysis of a non-oxide type of vertical-cavity surface-emitting laser (VCSEL) for operation at 850 nm. The modeling and characterization of the VCSEL is presented in the context of design considerations. Efforts are made to emphasize the behavioral features of the proposed VCSEL, in view of the analytical investigation, which has been performed through a series of simulations for various relevant parameters that are vital for the determination of the VCSEL characteristics. Some of these parameters are the intensity and refractive-index distributions, gain response, spontaneous emission, material gain variations, etc. The results obtained are compared with the oxide-confined VCSEL. It is observed that the proposed model of the VCSEL is suitable at the operating wavelength of 850 nm.     

Photochemical kinetics for holographic grating formation in phenanthrenequinone doped poly (methyl methacrylate) photopolymer

The photochemical kinetics of phenanthrenequinone (PQ) doped poly (methyl methacrylate) photopolymer in holographic recording was studied theoretically and experimentally. The diffusion of PQ molecules during holographic recording was negligible because of its small diffusion coefficient at room temperature. A photochemical reaction kinetics model of PQ/PMMA was established. The analytical expressions for the temporal variations of transmittance and diffraction efficiency were derived. By fitting the experimental curves, some parameters related with the polymer components were obtained by the proposed model, which can be used to analyze the photochemical process and will be helpful to the optimization of material preparation.     

Two-atom model for the calculation of surface blocking in medium and high energy ion scattering

A two-atom blocking model has been developed to analyze surface blocking patterns recently obtained in medium energy ion scattering experiments. In the model the mean square thermal vibration amplitude of a surface atom can be used as a fitting parameter in comparison with experimental results. Anisotropic surface vibrations have been taken into account by assuming a non-spherical Gaussian probability distribution for the thermal displacement of the surface atom. In addition, some analytical expressions have been derived for the effective nuber of target atoms contributing to the yield of ions backscattered into a blocking direction.     

Numerical modeling of the trajectories of plastic granules in a tribo-aero-electrostatic separator

A tribo-aero-electrostatic separator has been recently patented for the selective sorting of granular plastics mixtures generated during the recycling of waste electrical and electronic equipments (WEEE). The plastics are tribo-charged in a parallelepiped fluidized bed device, two opposite walls of which being the electrodes that generate the electric field that performs the separation. In two previous papers, different sets of operating parameters of this separator have been studied by hundreds of experiments, in order to improve the efficiency of the process and the purity of the products. The aim of the present paper is to complement these studies by establishing a model for computing the trajectory of plastics granules in such separator. The distribution of electric field and the profile of the airflow between electrodes were expressed using simple analytical formulas, which were introduced in the system of differential equations that served for the calculation of granule trajectories under the action of the various electric and mechanical forces. The computations were performed for various operating parameters: applied-voltage, granule size, charge density. The model can guide the design of industrial tribo-aero-electrostatic separators and the choice of the optimum values of the operating variables of such equipment.     

On the use of wavelength and time diversity in optical wireless communication systems over gamma–gamma turbulence channels

Optical wireless communication or free space optical systems have gained significant research and commercial attention in recent years due to their cost-effective and license-free high bandwidth access characteristics. However, by using the atmosphere as transmission media, the performance of such a system depends on the atmospheric conditions that exist between transmitter and receiver. Indeed, for an outdoor optical channel link, the existence of atmospheric turbulence may significantly degrade the performance of the associated communication system over distances longer than 1 or even 0.5 km. In order to anticipate this, particular attention has been given to diversity methods. In this work, we consider the use of wavelength and time diversity in wireless optical communication systems that operate under weak to strong atmospheric turbulence conditions modeled by the gamma–gamma distribution, and we derive closed form mathematical expressions for estimating the system's achievable outage probability and average bit error rate. Finally, numerical results referred to common practical cases are also obtained in order to show that wavelength and time diversity schemes enhances considerably these systems’ availability and performance.     

Monte Carlo simulation and parameterized treatment on the effect of nuclear elastic scattering in high-energy proton radiography

A version of Geant4 has been developed to treat high-energy proton radiography. This article presents the results of calculations simulating the effects of nuclear elastic scattering for various test step wedges. Comparisons with experimental data are also presented. The traditional expressions of the transmission should be correct if the angle distribution of the scattering is Gaussian multiple Coulomb scattering. The mean free path(which depends on the collimator angle) and the radiation length are treated as empirical parameters, according to transmission as a function of thickness obtained by simulations. The results can be used in density reconstruction, which depends on the transmission expressions.     

Fully analytical evaluation of optical gain coefficient in bulk semiconductors in quasi-equilibrium free-carrier approximation

In this letter, a new analytical method is presented to calculate of the semiconductor optical gain coefficient. This method is particularly suitable for theoretical analyses to determine the dependence of semiconductor gain on the total carrier density and temperature in the semiconductor lasers. Also, the optical gain functions for semiconductor optical gain coefficient are presented analytically. The analytical evaluation is verified with numerical methods, which illustrates the accuracy of these obtained analytical expressions.     

Diagram technique for finding of vertex functions in the Landau theory of heteropolymer liquids

The problem on finding the coefficients of the Landau free energy expansion into the power series of parameter of order has been considered for solutions and melts of linear heteropolymers whose molecules comprise several types monomeric units arranged stochastically. The presence of such a quenched structural disorder places this problem outside the framework of the traditional statistical physics inviting for its solution special approaches. One of them, based on the replica concept and actively engaged in theoretical physics of disordered systems, has been invoked in this paper to derive expressions for the vertex functions in the Landau theory of heteropolymer liquids. An algorithm has been formulated which permits one resorting to the simple diagram technique to write down expressions for these functions of any order in terms of the statistical characteristics of chemical quenched structure of polymer molecules. Explicit expressions for the contributions to the Landau free energy up to the fourth degree of order parameters for polymer systems with an arbitrary structural disorder have been presented to illustrate this general algorithm. Its potentialities have been also exemplified for the melt of random m-component copolymer where exact analytical formulas for these contributions up to n=6 at an arbitrary m have been derived for the first time.     

A new method of calculating the orbital angular momentum spectra of Laguerre-Gaussian beams in channels with atmospheric turbulence

Studying orbital angular momentum(OAM) spectra is important for analyzing crosstalk in free-space optical(FSO)communication systems. This work offers a new method of simplifying the expressions for the OAM spectra of Laguerre-Gaussian(LG) beams under both weak/medium and strong atmospheric turbulences. We propose fixing the radius to the extreme point of the intensity distribution, review the expression for the OAM spectrum under weak/medium turbulence,derive the OAM spectrum expression for an LG beam under strong turbulence, and simplify both of them to concise forms.Then, we investigate the accuracy of the simplified expressions through simulations. We find that the simplified expressions permit accurate calculation of the OAM spectrum for large transmitted OAM numbers under any type of turbulence. Finally,we use the simplified expressions to analytically address the broadening of the OAM spectrum caused by atmospheric turbulence. This work should contribute to the concise theoretical derivation of analytical expressions for OAM channel matrices for FSO-OAM communications and the analytical study of the laws governing OAM spectra.     

静电六极装置电场分布的数值计算方法及在N2O分子转动态选择、取向中的应用

阐述求解极性分子转动态选择及取向静电六极装置中势能分布、电场分布的数值计算方法.为了获得电场分布公式,需通过数值迭代求解势能满足的Laplace方程,获取数值分布点,通过数值分布点,由待定系数的多级展开势能解析表达式进行最小二乘拟合获得势能分布公式,由势能对空间向量的微分获得电场分布.分子在六极电场中的运行轨迹采用经典Newton方程描述,并通过四阶龙格-库塔方法(Four Order Runge-Kutta Method)实现数值求解,其中能量处理采用量子力学方法.应用此方法给出静电六极装置的电场分布公式,运用获得的电场分布公式计算和讨论电场对极性分子N₂O的静电六极转动态选择、取向所带来的影响.     

Improved Chernoff Bound of Gaussian Q-function with ABC algorithm and its QAM applications to DB SC and MRC systems over Beaulieu–Xie channels

In this study, we propose an improved upper bound for the Gaussian Q function by using artificial bee colony algorithm. Then, we investigate the performance of the dual-branch (DB) selection combining (SC) and maximal ratio combining (MRC) systems over the Beaulieu–Xie fading channels. The probability density functions of the instantaneous signal to noise ratio for the considered systems are obtained. Employing the proposed upper bound, we derive closed-form expressions of the error probability for the quadrature amplitude modulation (QAM) techniques such as rectangular QAM (RQAM), cross QAM (XQAM), and hexagonal QAM (HQAM). Furthermore, the asymptotic error probability expressions for the DB SC system are also obtained to simplify the analyses. The effects of some key parameters in the systems are shown in the results. Comparisons of the different modulation types and the different upper bound approaches for the Gaussian Q function are presented. Finally, it has been shown that the upper bound approximation presented in this study can be widely used for many communication applications.     

在XRF多变元体系因素分析中应用交互有效法选择体系的主组份

本文报道了在X-射线荧光分析多变元体系因素分析中,应用交互有效法选择体系主组份的研究。本方法在基本参数法的基础上,运用交互有效法,通过最小预报残差平方和(PRESS)的计算,对体系进行了主组份分析,确定了该体系中的最佳维数和主要影响因素。选择体系中的主组份进行回归分析,剔去了噪声,模型稳定性增强,XRFA的预报能力和分析结果准确度有了显著的提高。文中给出了分析地质样品中十三个主、次量元素的实验结果和数据对照。